Multiple wheel undercarriage for airplanes



March 3, 1953 J. H. GEissE 2,630,285

MULTIPLE WHEEL UNDERCARRIAGE FOR AIRPLANES Filed Dec. .19, 1950 3 Sheets-Sheet 1 INVEN TOR.

March 3, 1953 J. H. GEISSE 2,630,285

MULTIPLE WHEEL UNDERCARRIAGE FOR AIRPLANES 5 Sheets-Sheet 2 Filed Dec. 19, 1950 WIND INVENTOR.

March 3, 1953 J. H. GEISSE 2,630,235

MULTIPLE WHEEL UNDERCARRIAGE FOR AIRPLANES Filed Dec. 19, 1950 3 Sheets-Sheet 5 FIG-3.4:.

IN VEN TOR.

Patented Mar. 3, 1953 UNITED STATES TENT OFFICE MULTIPLE WHEEL UNDERCARRIA'GE FOR ,AIRPLANES .3 Claims. 1 My invention relates to undercarriages for airplanes in which four or more wheels, spaced :bo-th laterally and longitudinally, are attached to one strut and has for its objectives a reduction in undercarriage weight, improved cross wind 1an-da tionship to the longitudinal axis of the .airplane.

When so fixed the wheels, the strut to which they are attached, and the airframe are all subiiected to high side loads when the airplane is landed in a drift. The structure required to withstand these loads is heavy and the jolt :and the roll of I the airplane due to these high side loads :is discnn'certmg to the pilot and the passengers.

To the above difficulties, which are common :to all .fixe'd wheel mountings, the use of wheels spaced :fore and aft on -theirsupporting strut has introduced an additional problem. in the execution of turns on the ground these wheels must ski-d andskew. This imposes a high torque load on the strut which increases the strength and weight requirements and causes excessive wear of the tires.

I minimize these problems by applying to such undercarriages the type of cross wind undercarflag-e mechanism described in my Patent Number 2,529,933,datedNovember 14, 1 950.

The application is best described by reference to the accompanying drawings, "in which:

Figure 1 "is a side elevation and Figure 2 a plan viewof a typical arrangemen-t-o'f four wheels on one strut with :my mechanism added thereto.

Figure *3 is a "second plan view showing the relative position of the wheels in a drift landing and Figure 4 is a third plan view showing the positions of the wheelduring the execution of a turn on the ground.

Figure '5 is a detail of the collapsible part of the tie rods connecting the wheels.

In all figures, "I is the upper part of a convention-al shock strut in which the lower part 2 is reciprocatable. A conventional jack-knife element .3 prevents rotation of part .2 in part 'I. Attached to the lower end of :part 2 is a rectangu- *larlrame 4,. The frame 4 has spindle bearings 5 attached .aat its four corners. Rotatably :mounted in the --spindle bearings 5 .are the spindles 6 formed on the upper ends of the wheel forks 1. The wheel forks l are curved to provide castering action of the wheels a8.

Extending rearwardly from each wheel fork l they will do my mechanism.

( Cl. 24 i--103.-)

is an arm 9. The arms 9 of the rear wheels are interconnected by the crossed :tie rods H] which are pivotally attached thereto. The arms 9 of the front wheels are connected together in the same manner.

The tie rods I 0 are capable of foreshortening as shown in Figure .5. They are made up of two parts II and I2. Part I] has attached to it the cylinder I3 and part l2 'hasattached to it the collar or piston M which is reciprocata-ble in cylinder I 3.

The tie rods iii are crossed so that the nosing in of one wheel relative to its frame 4 will constrain the one connected .wit-h it to nose out to a greater degree than it has nosed in. Other types of wheel interconnection which would accomplish this relationship between inward and outward castering could be used without departing from the scope of this invention or the appended claims.

Patent No. 2,529,933, previously referred to, discloses that with this form of wheel interconnection the wheels will assume the position shown in Figure 3 and that there will be a side load on the inside of the nosed out wheel as indicated by the vector L in .Figure 3 and that a larger side load will be imposed on the nosed in wheel as indicated by the vector R.

The relative magnitudes of the side loads .R. and .L will be determined by the geometry of the wheel interconnections but the result-ant of these side loads will always be less than one half of the resultant side load which wouldprevail under the same degree of drift with fixed wheels.

In Figure 4 two assumed centers of path curvature are shown, one C ahead of the rear wheels and the other 0 in line with the centers of the rear wheels. The lines Tare tangents to circles drawn around the center C and passing through the centers of the rear wheels. From these it will be immediately apparent that minimum skewing of the rear wheels in a turn around center 0 would require that they assume a converging heading. However, .if they caster at all :my mechanism is such that they would have to assume a diverging heading. Hence, it is evident that any turnaround .a centerahead'of the rear wheels would be accompanied by a considerable skewing of the wheels.

The lines P are tangents to circles drawn around the center 0 and passing through the centers oi the front wheels. Here it will be apparent that minimum skewing would require the wheels to assume a diverging heading which Hence, the theory of least work will be satisfied only when the airplane turns around a center in line with the rear wheels.

In Figure 4 the angle of castering of the right front wheelin such a turn designated as an 3 and that of the left front wheel as (11.. The cornering angles, i. e. the angles between the wheel headings and their paths, are designated as an and CL. The latter are direct measures of the amount of skewing of their respective wheels.

The castering angles an and GL and the cornering angles eR. and a, are determined by the geometry of the wheel connecting linkage but as shown in the patent previously mentioned the ratio of the cornering angles will approximate the reciprocal of the ratio of the castering angles. Assuming the ratios to be K and l/K the values of an and 61. can be determined as follows:

It is apparent from the last equations and from Figure 4 that the skewing will be reduced to zero when (in equals K01. and that R will approach this equality as the radius of turn decreases. At larger radii 0R will approach equality with 01. and the sum of the cornering angles ER and 61. will approach For fixed wheels the corresponding sum of the cornering angles ER and er. would be equal to 20. Hence, the reduction in tire skewing in a turn on the ground accomplished by my mechanism would range from 100 per cent elimination to a reduction of over 50 per cent.

The reduction in torque on the strut would be substantially greater than the reduction in skewing. Whereas in calculating the total skewing the values of GR and EL are added, in the calculation of the torque they would be substractive since the moment of the side load of the right hand wheel around the strut center would be in the opposite direction to the moment of the side load of the left hand wheel.

In the castering of wheels shimmy is an ever present problem and in Figure 5 I have shown one simple method of dampening shimmy with the particular mechanism used to illustrate my invention. When the wheels caster one of the tie rods Ill must foreshorten and the collar or piston 14 will reciprocate in the cylinder l 3. Filling this cylinder with a suitable liquid and providing restricted passages 15 from one side of the piston 14 to the other side will provide a conventional hydraulic shimmy damper.

In most cases it is also desirable to provide some means of returning the wheels to their straight ahead position after they have left the ground. This could be accomplished readily by placing a spring [6 in the member I l and providing an extension to member 12 which would compress it when the tie rod l0 foreshortens.

A distinct advantage of my construction is that the mechanism which reduces the torque on the strut during turns on the ground is at the same time the mechanism which provides the needed caster restraint in cross wind landings. Any other form of caster restraint, such as springs and cams, would oppose the castering of the wheels in a turn on the ground with the same strength as they oppose castering during a drift landing.

My construction would have distinct advantages when used on airplanes having the socalled bicycle type of undercarriage in which the entire weight of the airplane is supported on wheels placed under the longitudinal axis of the airplane in fore and aft positions. In such airplanes it is all the more desirable to use additional wheels to distribute the weight and to caster the main wheels in arder to reduce the loading of the auxilliary outboard wheels.

Having thus described my invention, I claim:

1. An undercarriage element for aircraft comprising a frame adapted to be attached to the aircraft for the ground support thereof, multiple ground engaging wheels casterably mounted on said frame, said wheels being arranged in longitudinally spaced pairs, the wheels of each pair being spaced laterally, and linkage connected between the wheels of each pair constraining them to caster in the same direction, said linkage simultaneously constraining one of said wheels to toe out through a greater angle than the other toes in.

2. A ground engaging element for aircraft comprising a telescopic shock strut, a frame attached to the lower end of said strut, laterally spaced ground engaging wheels casterably mounted on said frame to the rear of the centerline of said strut, other laterally spaced ground engaging wheels casterably mounted on said frame to the front of the centerline of said strut, linkage connected between the wheels mounted to the rear of said strut, and other linkage connected between the wheels mounted to the front of said strut, said linkages constraining the wheels to which they are attached to caster in the same direction but in different amounts such that they toe out more than they toe in.

3. An airplane undercarriage element including a frame adapted to be attached to the air frame, multiple ground engaging wheels casterably mounted on said frame and disposed laterally and longitudinally with respect to each other and linkages connected between each of said wheels and its laterally spaced counterpart, said linkages constraining the wheels to which they are attached to assume diverging headings relative to each other when they are castered away from their straight ahead position.

JOHN HARLIN GEISSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,029,540 Porteous Feb. 4, 1936 2,346,667 Dowty Apr. 18, 1944 2,502,522 Hoobler Apr. 4, 1950 2,529,933 Geisse Nov. 14, 1950 2,538,388 Sievers Jan. 16, 1951 2,567,074 Kupiec Sept. 4, 1951 FOREIGN PATENTS Number Country Date 267,070 Germany June 6, 1912 

